I was carrying out maintenance of the biogas plant and unexpectedly a spanner slipped from my hand and fell into the digester. The tank was full of slurry and the gap between the digester and gas holder is also very narrow. Either I have to buy a new spanner or find out a way to retrieve the spanner from inside the digester.
Suddenly I got an idea. The spanners are attracted to magnets. Why not use a magnet to pull out the spanner from the tank ? The magnet I would use should be small enough to pass through the little gap. This should also be powerful enough to attract the spanner from the thick slurry and bring it back without dropping. A magnet with such characters is the small neodymium magnets present in the actuator arms of Hard disk drives. I have few old hard disk drives with me, so I can take apart one and collect the magnet.
Step 1: Dismantle Hard Disk and Remove Magnet
There are so many instructables on how to take apart a hard disk drive, so I am not going to repeat here again. I have dismantled my old hard disk drive and retrieved the magnet from it which you can see in the picture above. Using this I will make a metal detector which will find and pull out the spanner from inside the tank.
Step 2: Other Materials You May Need
In addition to the neodymium magnet I also need a stick which is longer than the height of the tank and few strands of copper wire to tie the magnet with the stick.
I have preferred to use a wooden stick rather than a pvc pipe as the stick will have more grip and the magnet will not slip from the stick and fall into the tank (then I will have to search for another method to retrieve the magnet also). I have used few strands of copper wire which was readily available with me. You can use anything you feel better to tie the magnet with the stick.
Step 3: Make the Tool
Here you can see that I have tied the neodymium magnet at one end of the stick with strands of copper wire. This small magnet is so powerful that it can lift heavy objects without dropping them.
Step 4: Retrieve the Spanner
The gap between the digester and gas holder is very narrow. So I have used a piece of PVC pipe between these two tanks to make a little bit more room. Then I inserted my home-made metal detector in the slurry and very slowly moved it back and forth nearer to where the spanner fell down.
Suddenly I could hear a clicking sound and felt little vibration in my hands. Slowly I lifted the stick and the spanner was there sticking to the magnet...!!!
Step 5: The Happy Ending
I have washed both the spanner and the stick with the magnet. The spanner will go back to where it belongs and the magnetic retriever will be added to the collection of tools I have.
The Happy Ending...